Ab Initio Study on Structures and Vibrational Spectra of M⁺(H₂O)Ar₂ (M = Cu, Au)

Abstract

Previous investigations have shown that it is difficult to acquire the infrared (IR) spectra of M⁺(H₂O) (M = Cu, Au) using a single IR photon by attaching an Ar atom to M⁺(H₂O). To explore whether the IR spectra can be obtained using the two Ar atoms tagging method, the geometrical structures, IR spectra and interaction energies are investigated in detail by ab initio electronic structure calculations for M⁺(H₂O)Ar₂ (M = Cu, Au) complexes. Two conceivable isomeric structures are found, which result from different binding sites for two Ar atoms. CCSD(T) calculations predict that two Ar atoms are most likely to attach to Cu⁺ for the Cu⁺(H₂O)Ar₂ complex, while the Au⁺(H₂O)Ar₂ complex prefers the isomer in which one Ar atom attaches to an H atom of the H₂O molecule and the other one is bound to Au⁺. Moreover, the calculated binding energies of the second Ar atom are smaller than the IR photon energy, and so it is possible to obtain the IR spectra for both Cu and Au species. The changes in the spectra caused by the attachment of Ar atoms to M⁺(H₂O) are discussed.

Keywords:

• M⁺(H₂O)Ar₂(M = Cu, Au) complexes
• binding energies
• infrared spectra
• isomers

Acknowledgement

The authors acknowledge the support by the National Natural Science Foundation of China (Grant No. 10274015) and the Science Foundation of Harbin Institute of Technology, China. Calculations with the Gaussian 03 program were performed on computers of the National Laboratory of Theoretical and Computational Chemistry, Jilin University, China.